The present invention pertains generally to medical devices and more particularly to medical devices for monitoring activity of the heart and providing therapy thereto including implantable cardiac pacemakers and external programmers and other devices for determining optimal pacing parameters for such implantable pacemakers and for providing such pacing parameters to an implanted device.
Various types of medical devices are employed to monitor electrical or other activity of the heart and to provide therapy to the heart for the correction of electrical conduction defects, inadequate pump function, or irregular cardiac rhythms. Such defects and irregular rhythms may result from or indicate various pathological conditions of the heart, including congestive heart failure. Many such devices are implantable beneath the skin of a patient, i.e., in the patient""s chest. Such implantable devices include a hermetically sealed canister containing electronic circuitry for implementing the functions of the device, one or more electrodes implanted in one or more of the ventricles and/or atria of the heart, or in close proximity thereto, and leads for connecting the electrodes to the circuitry within the device canister. The device circuitry includes circuitry for detecting electrical signals produced by the heart, which signals are picked up at the electrodes, along with circuitry, typically implemented in a microprocessor, for analyzing the thus detected cardiac signals. The device may also include circuitry for providing therapy in the form of electrical signals applied to the heart. Such signals are provided to the heart via the leads and electrodes mounted in the heart so as to correct electrical conduction defects or abnormal rhythms. The analysis circuitry controls the delivery of such electrical therapy signals based on the detected cardiac activity signals. The implantable device may also include a transmitter/receiver for transmitting cardiac activity and other information to an external device for, e.g., storage and/or further analysis, and for receiving information, such as programming instructions, from the external device via, for example, an RF link.
An example of such an implantable cardiac device is an implantable cardiac pacemaker. A pacemaker provides relatively low-level electrical pulses to the heart to stimulate heart activity when the natural cardiac rate provided by the heart is too low. A dual chamber pacemaker includes electrodes positioned in both the atria and ventricles of the heart for detecting naturally occurring atrial and ventricular activations, and for providing pacing pulses to the atria and/or ventricles as needed. Such a device monitors the time between sensed and paced atrial and ventricular activations and provides pacing pulses as needed to maintain an adequate heart rate. For example, such a device will note the occurrence of a sensed or paced atrial or ventricular event and, if a subsequent naturally occurring atrial and/or ventricular event is not sensed within a certain time (escape interval) following the first sensed or paced event, a pacing pulse will be applied to the atria and/or ventricles to maintain a desired heart rate.
Implantable cardiac pacemakers may also be employed to improve cardiac function in heart failure patients. Such implantable pacemakers may improve cardiac pump function by correcting left ventricular conduction system defects. In such systems an electrical pacing signal is provided by the pacemaker to a pacing lead implanted epicardially in the coronary vein to stimulate the left ventricle. Biventricular pacing may also be provided. Such heart failure therapy is commonly referred to as cardiac resynchronization therapy. Implantable pacemakers for heart failure therapy may be implemented as dual or triple chamber pacemakers. Such pacemakers may be included within an implantable device capable also of providing atrial and/or ventricular defibrillation.
As discussed above, left ventricular or biventricular pacing can have a beneficial effect for patients suffering from congestive heart failure. However, it has been found that the various parameters which control such pacing must be set within a certain range for such pacing to have a beneficial effect for those patients, or to yield the best therapeutic response. For example, it has been found that patients exhibiting congestive heart failure have a specific range or value of AV delay (the maximum time allowed to pass following a sensed or paced atrial event before the ventricles are paced), over which the therapeutic response to pacing is positive. Also, within the range of AV delay, or other pacemaker settings, for which a positive therapeutic effect is provided by pacing, is a more narrow optimum subrange of AV delay or other pacing parameter values which provide the greatest degree of therapeutic improvement. Arbitrarily setting the AV delay and other pacing parameters at nominal values may not guarantee the optimum benefit obtainable (or even any benefit at all) by left ventricular or biventricular pacing in congestive heart failure patients. It would, therefore, be advantageous to have a system which allows an operator to determine whether a controlled pacing parameter or set of parameters is optimal for a given patient and, if not, which allows the operator to reprogram an implanted pacemaker such that the implanted device is made to operate in a pacing mode and with pacing parameters that result in an optimum benefit to the patient.
U.S. Pat. No. 5,540,727 to Tockman, et al. describes a method and apparatus for optimizing the pacing mode and pacing cycle parameters of an implanted dual chamber pacemaker. This patent describes providing as inputs to an external monitor/programming device data from one or more cardiac performance monitoring devices. Such devices may include external equipment, such as an acceleration sensor, capable of providing signals characteristic of features of the mechanical movements of the heart muscle, its valves, and the blood being pumped by it, a Doppler flow sensor for sensing cardiac output, a pressure cuff or similar type sensor for providing an indication of mean arterial pressure, a pulse oximeter to provide signals corresponding to the percentage concentration of oxygen and carbon dioxide in the patient""s blood, and/or a respiration sensor capable of analyzing respiratory gases and delivering signals proportional thereto to the monitor/programmer. One or more sensors may also, or alternatively, be implanted within the body to sense various cardiac performance parameters and to provide corresponding data to the monitor/programmer. Data from the cardiac performance monitoring devices is used by the monitor/programmer to monitor one or more physiological parameters during a pacing interval with a given pacing parameter (e.g., AV delay) set at a given value and with a given pacing mode. The selected pacing parameter is changed incrementally, and monitoring of the detected physiological parameters is repeated at each increment of the pacing parameter. Between each such pacing period, the heart is allowed to beat at a natural sinus rhythm, in order to establish a baseline for comparison. The physiological parameters monitored during each pacing interval are analyzed to determine the selected pacing parameter value and pacing mode which results in the best resulting physiological response, which could be either a maximum or minimum value of a physiological parameter, depending upon the particular physiological parameter involved. An implanted pacemaker is then programmed using the external programmer to operate with the pacing parameter value and pacing mode associated with the best determined physiological parameter response.
A known method of evaluating heart mechanical performance is described in U.S. Pat. No. 5,291,895 to McIntyre. This patent describes a system for evaluating cardiac performance which employs a finger pressure sensor including a piezoelectric pulse pickup and an inflatable cuff which wraps around a patient""s finger to apply pressure, through the pickup, to the skin of the patient""s finger. Pressure pulses detected using the finger sensor may be analyzed to detect abnormal cardiac performance. In particular, abnormal cardiac performance may be identified by analyzing the finger pressure signal obtained during and after an activity which produces stress on the patient""s heart. An example of such a heart-straining activity is the Valsalva maneuver, in which a patient exhales forcefully into a closed system so as to maintain an increased intrathoracic pressure for a short period of time. It has been determined that the reflected arterial-pulse contour detected from a patient""s finger during the Valsalva maneuver is predictive of pulmonary-capillary wedge pressure. In particular, the pulse-amplitude ratio of the final (minimal) to initial (maximal) amplitude of the strain phase of the maneuver has been determined to correlate well to pulmonary-capillary wedge pressure. Pulmonary-capillary wedge pressure is a well-known measure of heart failure disease.
What is desired is a system and method which allows a physician to easily, accurately, and noninvasively monitor the condition of a heart failure patient and to optimize the pacing parameters of an implanted pacemaker used to treat such a condition. In particular, what is desired is a system and method which allows a physician to monitor the condition of a heart failure patient and to optimize the pacing parameters in an implanted pacemaker providing therapy to the patient by noninvasively monitoring a physiological parameter related to heart performance and programming the implanted device to optimize such a parameter.
The present invention provides a method and apparatus for monitoring the condition of a heart failure patient and for determining optimal pacing parameters for an implanted cardiac pacemaker based on noninvasive monitoring of physiological parameters related to heart performance. In particular, the present invention features an external programmer device for monitoring the progression of heart failure disease in a patient and/or transmitting programming instructions to a pacemaker device implanted in the patient to optimize one or more pacing parameters thereof. A finger sensor, such as a photoplethysmogram detector, is provided, which may be clipped to the tip of a finger of a patient in which a pacemaker is implanted. The finger sensor is coupled to the external programmer device to provide a plethysmogram signal thereto. The finger plethysmogram signal is analyzed using the external programmer device to determine and monitor cardiac performance from characteristics thereof. The external programmer device may be employed to program one or more pacing parameters (e.g., the AV delay, the pacing chambers, etc.) in the implanted device, such that the performance of the heart, as indicated from the detected finger plethysmogram signal, is optimized. Cardiac performance parameters monitored via the finger plethysmogram signal in accordance with the present invention also may be employed to determine the optimum location for the placement of cardiac pacing electrodes at the time of implant.
Various physiological characteristics may be non-invasively monitored, e.g., using a finger plethysmogram signal, analyzed to determine cardiac performance and, in turn, used to optimize implanted cardiac pacemaker device pacing parameters in accordance with the present invention. For example, heart failure patients with advanced ventricular dysfunction often exhibit pulsus alternans, i.e., pressure pulses that alternate in amplitude: strong, weak, strong, weak. Pulsus alternans can be observed non-invasively, e.g., using the finger plethysmogram, and the progression of heart failure monitored by observing the presence of pulsus alternans in the finger plethysmogram signal provided to an external programmer device. The external programmer device may be used to adjust the pacing parameters of an implanted pacemaker to minimize the pulsus alternans as non-invasively identified, e.g., in the finger plethysmogram signal.
Atrial fibrillation patients experience irregular beat-to-beat blood pressure changes. Such pressure changes may be non-invasively identified, e.g., from a finger plethysmogram signal. A finger plethysmogram signal may thus be used by an operator of an external programmer device, in accordance with the present invention, to monitor the progression of heart failure and to adjust an implanted pacemaker""s pacing parameters such that the blood pressure of the atrial fibrillation patient is regularized, resulting in a plethysmogram signal with more uniform peak amplitudes. Such plethysmogram information could also be combined with ventricular rate information to optimize the pacing parameters of a pacemaker implanted in an atrial fibrillation patient.
A finger plethysmogram signal provided to an external programmer device in accordance with the present invention may also be used to monitor filling pressures, such as pulmonary-capillary wedge pressure, which is a common measure of a patient""s hemodynamics that is an approximation to the left ventricular diastolic end pressure. As discussed above, pulmonary-capillary wedge pressure (filling pressure) is a well-known measure of heart failure disease. In accordance with the present invention, pulmonary-capillary wedge pressure (filling pressure) may be monitored non-invasively, e.g., using a finger plethysmogram signal or other blood pressure related signal obtained during the performance of a classic Valsalva maneuver by a patient. Performance of the Valsalva maneuver may preferably be monitored by the external programmer device to which a finger plethysmogram signal is provided. For this purpose, a mouthpiece may be provided coupled to the external programmer device, and a pressure sensor providing a pressure signal to the programmer device coupled to the mouthpiece for determining the patient""s intrathoracic pressure during performance of the Valsalva maneuver. The intrathoracic pressure signal may be employed by the external programmer device for monitoring the patient""s performance of the Valsalva maneuver. An external programmer device in accordance with the present invention may employ the finger plethysmogram signal generated during the Valsalva maneuver to monitor the progression of heart failure in a patient, either by qualitative observation of the shape of the finger plethysmogram signal during performance of the Valsalva maneuver or by quantitative estimate of filling pressure derived therefrom in a conventional manner. The external programmer device may be employed to program one or more pacing parameter of a pacemaker implanted in a patient in a manner such that the finger plethysmogram signal generated during the Valsalva maneuver is made more normal, i.e., the qualitative shape of the finger plethysmogram signal is more normal or the quantitative pulmonary-capillary wedge pressure (filling pressure) estimated therefrom is minimized.
Various different procedures may be employed for optimizing the pacing parameters of an implanted pacemaker in accordance with the present invention, depending upon the cardiac performance parameters non-invasively monitored, e.g., using a finger plethysmogram signal provided to an external programmer device. For example, if the finger plethysmogram signal is employed to monitor filling pressure (either qualitatively or quantitatively), a clinician may employ the present invention to monitor and store the plethysmogram signal obtained from a patient performing the Valsalva maneuver for a given set of pacemaker pacing parameters, and then send the patient home. After a few days, needed to reach a steady state fluid balance, the patient would return, a finger plethysmogram obtained while the patient performed the Valsalva maneuver again, and further adjustments to the pacemaker pacing parameters made using the external programmer device, as necessary. After several such trials, the optimum pacing parameters to be programmed into the pacemaker device may be selected as those yielding the best finger plethysmogram response during the Valsalva maneuver, e.g., the parameters yielding the best pulmonary-capillary wedge pressure. The Valsalva response in the finger plethysmogram signal may also be observed, and/or the pulmonary-capillary wedge pressure derived therefrom, using a programmer device in accordance with the present invention, for monitoring disease progression of a patient, so that a deterioration can be better detected and characterized. Such monitoring may result in a determination that the patient""s disease may be managed more thoroughly with therapies other than, or in addition to, cardiac pacing.
Optimum pacing parameters may be determined, e.g., automatically using the external programmer device in a single diagnostic session. For example, the external programmer device may control an implanted pacemaker to pace a patient""s heart using a series of different pacing parameter values. The resulting finger plethysmogram signal obtained during each such pacing interval may be analyzed and stored. Between each such pacing interval, the heart may be allowed to beat at a natural sinus rhythm, in order to establish a baseline for comparison. Baseline beat amplitudes and repeated pacing intervals for each pacing parameter value under test may be employed in the determination of the cardiac effect of pacing as reflected in the finger plethysmogram signal, such that the effects of noncardiogenic changes on finger pulse amplitude and other artifacts are rejected. After cycling through various pacing parameters in this manner, the resulting finger plethysmogram signals stored may be analyzed, and the implanted pacemaker programmed either manually or automatically with the pacing parameters resulting in the plethysmogram signal indicating the best cardiac performance, e.g., the finger plethysmogram signal indicating the largest pulse amplitude response, eliminated or reduced pulsus alternans, or, in the case of a patient with atrial fibrillation, the finger plethysmogram signal with the most uniform peak amplitudes, i.e., indicating reduced irregular pressure changes.
A system and method in accordance with the present invention may be used to optimize any of several different pacing parameters to optimize pacemaker performance. Such parameters may include, for example, the AV delay, pacing mode, pacing power (e.g., pacing pulse amplitude and/or pulse width) and/or pacing location (left and/or right ventricle). In general, the present invention may be used to optimize any programmable pacing parameter which would result in a hemodynamic response. A system and method in accordance with the present invention also may be employed in the manner described to determine the optimum location for the placement of cardiac pacing electrodes at the time of implant.
Further objects, features, and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings.